When an innocent man going about his business is shot dead on a London tube, seven bullets pumped into his brain at near point-blank range, some would call it an execution. Others, though, claim it as a "lawful killing".

Thankfully, the jury at the inquest into the shooting of Jean Charles de Menezes rejected this interpretation. For three-and-a-half years his family members have patiently awaited their day in court, hoping that an inquest would finally deliver justice. By returning an open verdict yesterday the jurors went as far as they could after their hands were tied by the coroner.

Not only did he stop the jury giving an unlawful killing verdict, he also denied them an opportunity to spell out the reasons they found for Jean Charles's death. The only scope was a series of yes/no answers to apparently self-evident questions - yet the jurors could not decide whether the suicide attacks that preceded the shooting put pressure on the police. Further, they rejected much of the police version of events, including claims that officers shouted "armed police" before shooting. In that context, this is another damning indictment of the police.

What the jury above all refused to accept was the coroner's definition of a lawful killing: that it was more likely than not that the two police marksmen honestly, although mistakenly, believed that Jean Charles was a suicide bomber about to detonate a bomb. Jean Charles bore only a passing resemblance to the actual suspect, Hussain Osman; and his allegedly suspicious behaviour amounted to getting off a bus, seeing that the tube was closed and getting back on the bus while using his mobile phone. Even in the London of July 2005, on high alert after failed suicide bomb attacks, could such an appalling error be lawful?

The circumstances of Jean Charles's death have already been the subject of a number of reports and investigations by the police, the Independent Police Complaints Commission, the Crown Prosecution Service and the Metropolitan Police Authority, but the only prosecution that arose was for breaches of health and safety legislation. His family wanted individual officers to be held criminally accountable. They believed an inquest would achieve truth and justice. Instead, the coroner has presided over a whitewash.

At least, for the first time, the family had the opportunity to ask testing questions of many officers, from senior commanders to those who fired the fatal shots. The evidence has exposed a catalogue of errors at every level of the operation, and we learned a great deal about how Jean Charles was killed.

There was sufficient evidence to enable the jurors to return an unlawful killing verdict - and the open verdict suggests they may well have done so, given the chance. And there was ample evidence for a narrative verdict to catalogue the series of police failings causing or contributing to Jean Charles's death.

This 10-week inquest has been a fairly thorough inquiry, yet on an unequal field. The family were represented by a team of two barristers and solicitors, compared with the 10 barristers and several solicitors representing the police. The five police teams, supposedly representing separate interests, in reality worked together. On each occasion that a significant fault was exposed by Michael Mansfield's cross-examination, up to five barristers for the police would seek to undermine what had been exposed. By the time it came to making legal submissions on verdicts, the police teams effectively carved up the terrain. The family sought to challenge the ruling. But when an emergency application to the high court failed, they instructed their legal team to withdraw from the inquest, outraged by the limits the coroner placed.

At the end of this entire process, no one has faced any kind of appropriate sanction. Not one police officer involved in the operation has been subjected to disciplinary action. The two most senior officers have been promoted.

The inquest heard that Jean Charles once praised the restraint of the British police and reassured his mother they were not like their trigger-happy Brazilian counterparts. Yet we now know that, only a day or so before the fatal shooting, Ian Blair, the former Metropolitan police commissioner, met the prime minister and discussed ways to secure legal immunity for firearms officers during a heightened terrorist alert. He needn't have bothered: the police have effective immunity from prosecution, as this case has illustrated. Where an innocent man is killed in the cause of protecting the public, no coroner will allow the police to be held accountable.

Yesterday, though, ordinary men and women gave their verdict - and it was the best one possible, given the severe restrictions. It gives the family new hope that British justice might be true to its reputation, and they will seek a judicial review.

• Harriet Wistrich is the solicitor for the De Menezes family, whose campaign website is www.justice4jean.org